1. Field of the Invention
The present invention relates to a cellular Code Division Multiple Access (CDMA) communication terminal. More particularly, the present invention relates to a method and an apparatus for encoding/decoding transmission information.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) is a third generation (3G) mobile communication system which uses a Wideband Code Division Multiple Access (W-CDMA) scheme and is based on Global System for Mobile communication (GSM) and General Packet Radio Services (GPRS), which are European mobile communication systems. The UMTS provides a consistent service by which users of mobile phones or computers can transmit packet-based data and digitalized voice, video and multimedia data at a high speed of at least 2 Mbps anywhere throughout the globe.
The UMTS system uses an Enhanced Uplink Dedicated Channel (EUDCH or E-DCH) as a transmission channel in order to improve performance of packet transmission in the uplink, that is, in a transmission from a User Equipment (UE) to a Base Station (BS or node B). In order to support more stable high speed data transmission, the E-DCH supports technologies such as Adaptive Modulation and Coding (AMC), Hybrid Automatic Retransmission Request (HARQ), shorter Transmission Time Interval (TTI), and so forth.
The AMC is a technology which improves the efficiency in the use of resources by determining the modulation scheme and coding scheme of a data channel according to the channel state between a node B and a UE. A Modulation and Coding Scheme (MCS) is a combination of the modulation scheme and coding scheme, and various MCSs can be defined according to the supportable modulation schemes and coding schemes. The AMC adaptively determines the MCS level according to the channel state between the UE and the node B, thereby improving the efficiency in the use of the resources.
The HARQ is a technology of re-transmitting a packet in order to compensate for an erroneous data packet when an initially transmitted data packet comprises erroneous data packet. The HARQ scheme can be classified into a Chase Combining (CC) scheme by which packets in the same format as that of the erroneous initial packets are retransmitted, and an Incremental Redundancy (IR) scheme by which packets in a format different from that of the erroneous initial packets are retransmitted.
Further, the E-DCH permits a TTI shorter than 10 ms, which is the minimum TTI length presented by Release 5 (Rel 5) of the 3rd Generation Partnership Project (3GPP), thereby reducing the retransmission delay time and achieving a high system throughput.
A node B control scheduling is a scheme for data transmission using the E-DCH, in which a node B determines whether to transmit uplink data, an upper limit for an available data rate, and so forth, and transmits the determined information as a scheduling command to a UE, and the UE determines the data rate of the uplink E-DCH with reference to the scheduling command and transmits data by the determined data rate.
According to the node B control scheduling, a lower data rate is allocated to UEs located away from a node B within a range capable of preventing a value of noise rise or Rise over Thermal (RoT) measured by the node B from exceeding a target value, and a higher data rate is allocated to UEs located near the node B, in order to improve the performance of the entire system. The RoT represents radio resources used in the uplink by the node B and is defined by Equation (1) below.RoT=Io/No  (1)
In Equation (1), Io denotes a power spectral density for the entire reception band of a node B, which corresponds to the quantity of all uplink signals received by the node B, and No denotes a thermal noise power spectral density of the node B. Therefore, the maximum allowable RoT represents the entire radio resources which the node B can use in the uplink.
FIG. 1 is a flow diagram of transmission and reception that is achieved through a typical E-DCH.
First, in step 102, the node B and the UE set up an E-DCH. The setup step 102 comprises the transmission of messages through a dedicated transport channel. When the setup of the E-DCH has been completed, the UE reports scheduling information to the node B in step 104. The scheduling information comprises UE transmission power information representing uplink channel state, information of extra power transmissible by the UE, the quantity of data accumulated for transmission in a buffer of the UE, and so forth.
After receiving scheduling information from a plurality of UEs during communication, the node B monitors the scheduling information of the UEs, so as to schedule data transmission of each of the UEs in step 106. Then, the node B determines to allow uplink packet transmission of the UE and transmits a scheduling allocation command to the UE in step 108. The scheduling allocation command comprises scheduling allocation information which instructs the increase/maintenance/decrease of the maximum allowable data rate to the UE, or instructs the maximum allowable data rate or the timing for allowed transmission to the UE.
The UE determines the Transport Format (TF) of the E-DCH to be transmitted through uplink based on the scheduling allocation command in step 110, and transmits TF-related information in step 112 and uplink packet data through the E-DCH to the node B in step 114. The TF-related information comprises Enhanced Transport Format Indicator (E-TFI) which represents information of resources necessary in demodulating the packet data of the E-DCH. In step 114, the UE selects an MCS level in consideration of the channel state and the maximum allowable data rate allocated by the node B and transmits the uplink packet data by the MCS level.
In step 116, the node B determines if there is an error in the TF-related information and the packet data. In step 118, the node B transmits through an ACK/NACK channel to the UE, a Negative Acknowledgement (NACK) when any of the packet data has an error and an Acknowledgement (ACK) when none of the packet data has an error. When the node B has transmitted an ACK, which means completion of the packet data transmission, the UE transmits a new user data through the E-DCH. However, when the UE has received a NACK, the UE retransmits a packet data having the same content through the E-DCH.
In the environment as described above, in order to perform efficient scheduling, the node B allocates a low data rate to a UE farther away from the node B or a UE in a bad channel condition or a UE for receiving a service having a low priority, and allocates a high data rate to a UE near the node B or a UE in a good channel condition or a UE for receiving a service having a high priority, in consideration of the buffer state and power state of the UE and the RoT, and so forth, thereby improving the performance of the entire system.
In order to support the E-DCH operated as described above, the UE must report the scheduling information to the node B as performed in step 104. As described above, the scheduling information comprises UE transmission power information representing the uplink channel state, information of extra power transmissible by the UE, the quantity of data accumulated for transmission in a buffer of the UE, and so forth.
Accordingly, there is a need for a system and method to provide a specific channel encoding scheme for transmitting and receiving information having a predetermined size such as the scheduling information and the TF-related information.